In an optical transport network (OTN), data are commonly transmitted from a transmitter to a receiver by modulating an optical carrier light with digital information to generate an optical signal, which is then transmitted through an optical link to a receiver. At the receiver, the optical signal impinges on photodetectors, which generate photocurrent. The photocurrent is then processed to recover the data. In a coherent receiver, this processing typically uses a Digital signal processor (DSP) cascaded with a Forward Error Correction (FEC) decoder block. The DSP typically performs Analog-to-Digital Conversion (ADC), chromatic dispersion (CD) compensation, symbol clock recovery, polarization demultiplexing and Polarization Mode Dispersion (PMD) compensation, Frequency Offset Compensation, carrier phase recovery and finally symbol detection. The FEC block processes the detected symbols to recover the transmitted data.
In practical OTN systems, the data includes subscriber data and overhead data. The overhead data includes Operations Administration and Management (OAM) signaling that is used to control the optical link between the transmitter and receiver. Typically, the OAM signalling is included as a tributary data stream with the subscriber data modulated on the optical signal.
A limitation of this arrangement is that the DSP and FEC block must be fully operational at all times, even when there is little or no information is transmitted, causing a significant increase in power consumption.
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